As an internal combustion engine to be mounted in a vehicle, there has hitherto been known an internal combustion engine including a hydraulic-drive valve timing adjustment device for changing valve timing for intake and exhaust valves, and a lock mechanism for holding a rotation phase of a camshaft in an intermediate lock phase between the most advanced phase and the most retarded phase by means of a lock pin. Further, it has been proposed that in such a system, the internal combustion engine is started in the intermediate lock phase, and a shift then is made to a phase feedback control mode for controlling the rotation phase of the camshaft by a target phase in accordance with an operation state of the internal combustion engine (e.g., see Patent Literature 1). Patent Literature 1 discloses that an oil filling mode for filling an advancement chamber and a retardation chamber with hydraulic oil is performed before the shift to the phase feedback control mode. Further, Patent Literature 1 discloses that one oil control valve (OCV) performs an appropriate switch to any of a lock mode, the oil filling mode, and the phase feedback control mode, thereby adjusting inflow and outflow of the hydraulic oil to and from the valve timing adjustment device and the lock mechanism.
In order to promptly make a shift to the phase feedback control mode after starting of the internal combustion engine, it is desirable to quickly complete oil filling of the advancement chamber and the retardation chamber. It is thus considered that, in the oil filling mode, a spool position is moved to a region where a large amount of the hydraulic oil is supplied to the advancement chamber and the retardation chamber, and then oil filling is performed. Meanwhile, oil leakage may be apt to occur inside the oil control valve depending on a state of the hydraulic oil, and the oil leakage inside the valve may cause the hydraulic oil to flow into a portion originally to be blocked from inflow of the hydraulic oil, resulting in generation of a concern about erroneous release of the lock pin.